Simulation is an area of computer graphics that places high demands on the ability to generate lifelike images, sometimes as close to an actual photograph as possible, and also to be able to do so as quickly as possible or using the least amount of system resources. A particular challenge in simulation is to generate a plausible appearance—and in animated sequences, behavior—of fluid materials, for example smoke or water, taking into account practical limits for how much system resources can be used and how rapidly the simulation should be generated.